Method of fractionating vapors



F. v. ATKESON 2,330,326

METHOD OF FRACTIONATING VAPORS Filed May 10, 1941 Sept. 28, 1943.

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Patented Sept. 28, 1943 2,330,326 METHOD OF FRACTIONATING VAPORS Florian V. Atkeson, Pasadena, Calif. Application May 10, 1941, Serial No. 392,932

4 Claims.

My invention relates to a method of and apparatus for fractionating vapors. While my invention is capable of application to the separation of any mixture of vapors of different molecular weights, it finds particular utility in the fractionation of hydrocarbon vapors, and for i1lustrative purposes its application to such use is hereinafter described without limiting the invention to such application.

The objects of my invention include a substantial increase, within a compact apparatus of small size, of the area of contact of reflux liquid with the vapors during fractionation and a substantial increase in the surface area of the apparatus at a different temperature from the vapors and contacted by the vapors as compared with the conventional fractionating apparatus, such as a bubble tower. Another object of my invention is the easier control of the temperature gradient during fractionation of a mixture of vapors, which my invention contemplates providing by defining a long path of travel for the vapors within a compact apparatus and by subjecting each cross section of the stream of the mixture of vapors to a temperature gradient facilitating their selective condensation.

Another object or my invention is to provide a method of and apparatus for accurately and completely condensing selectively a mixture of vapors having condensing points differing only slightly.

Another purpose of my invention is the provision of a method of and apparatus for i'ractionally condensing a mixture of vapors of different condensing points either in one apparatus, from which condensates of different condensing points are withdrawn at diiierent levels, or in a plurality of devices, through which the vapor mixture is passed successively and from each of which a condensate having a predetermined range of condensing points is withdrawn.

Other obiects of my invention include the provision of an apparatus for fractionating vapors of differentcondensing points which is compact in size and inexpensive in manufacture.

Embodiments of my invention capable of performing these objects and providing these advantages and others are described in the following specification, which may be more readily understood by reference to the accompanying drawing in which Fig. 1 is a vertical sectional view of one embodiment of my invention;

Fig. 2 is a hori ontal sectional view taken as indicated by the e 2--2 of Fig. 1; and

Figs. 3, 4, and 5 are fragmentary vertical sectional views of other forms of my invention.

Referring to the drawing, which is for illustrative purposes only, the numeral I l indicates a fractionating apparatus which includes a tower l2, having a domed top i3, and a bottom plate It having a central opening l5 communicating through a depending bafile l6 with a bubble plate chamber H. The bubble plate chamber I1 is provided with a plurality of bubble plates [8. illustrated as three in number, each of which includes an upwardly projecting vapor pipe l9 with a cap 20 positioned over the upper end thereof and extending downwardly therearound to adjacent the upper surface of the bubble plate l8, so that vapors passing upwardly through the pipe l9 are directed downwardly through liquid upon the bubble plate I8 before continuing their passage upwardly to the tower i 2. Each bubble plate IB is provided with a liquid pipe l9a having a cap 20a for passingliquid downwardly therethrough, the bubble plates l8 acting to smooth out the flow of vaporsbefore the vapors enter the tower l2, making the rate of passage of the vapors through the tower more uniform and limiting the vapors entering the tower to those having the desired range of condensing temperatures.

The fractlonating apparatus ll includes also a kettle or still 2| positioned below and communicating with the bubble plate chamber l1. The still 2| may be heated in any suitable manner, as for example, by a steam coil 22, and is provided with an outlet pipe 2 la in the bottom thereof for withdrawing residue therefrom. A liquid supply pipe 23 is provided for supplying liquid to the still 2| for vaporization therein and may be connected to the bubble plate chamber 11 above the lowermost of the bubble plates l8, so that the incoming liquid oil exerts a reflux action upon the upwardly travelling vapors from the still 2|.

Provided within the tower I2 is a vapor line in the form of a coil of pipe 24 of metal of good heat conductivity, such, for example, as copper. The coil 2! is formed so that adjacent convolutions are in contact with each other and so that its lower end communicates with the central opening l5 of the bottom plate Id of the tower l2. The upper end of the coil 24 is connected to a riser pipe 25, which communicates through a pipe 26 with a condenser 21 of conventional construction or another iractionating device similar to the fractionating device H.

Positioned within the tower I! with its outer wall in contact with the coil 24 is a cooling jacket 42 annular in cross section and including an inner wall 34, an outer wall 44, and top and bottom walls 45 and 18, respectively. An inlet pipe 41 extends through the wall of the tower l2 and communicates with the cooling Jacket 22 near the upper end wall 35, and an outlet pipe 38 communicates with the cooling jacket 32 adjacent the lower end wall Ill.

The coil 24 is formed so that its external diameter is substantially less than the internal diameter of the tower l2, and the space between the vertical coil 24 and the wall of the tower i2 is filled with a heat insulating material 39 extending from the bottom plate l4 of the tower I2 to a top plate 40 which extends between the upper end of the cooling jacket 32 and the periphery of the domed cover it.

As illustrated, the condenser 21 includes inlet and outlet pipes 28 and 28, respectively, for supplying a cooling medium around a plurality of vapor pipes within the condenser 21, an outlet pipe 30 for withdrawing the liquid condensate therefrom, and an outlet pipe St for withdrawing from the condenser any uncondensable gases.

In performing the method of my invention with the apparatus described, the liquid to be fractionated is introduced through the inlet pipe 23 and passes downwardly through the bubble plates ill to the still 2|, where it is vaporized by the heat provided by the steam coil 22. The vapors pass upwardly through the vapor pipes ill in the Fill bubble plates IB, under the bubble caps 20 and I through the liquid upon the upper surface of the bubble plates l8, thus intimately commingling with the liquid. This commlngling of the vapors with the liquid serves to condense and lead, with the incoming liquid to the still 2i, vapors of the hydrocarbons of high condensing points, and serves also to preheat the incoming liquid before it reaches the still 2i.

From the bubble plate chamber ii the vapors pass upwardly through the baille it into the lower end of the coil 24. The vapors entering the coil 24 consist of a mixture of hydrocarbons of different condensing points. As this mixture passes upwardly through the coil 24, it is subjected to a cooling action by the liquid in the cooling jacket 32. The outer wall 34 of the cooling jacket 32 being in intimate contact with the inner surface of the coil 24 and, if desired, the space between each pair of adjacent turns of the coil 24 and such outer wall 34 being filled with a suitable metal of high conductivity, the cooling liquid within the jacket 32 is maintained in intimate heat conducting relationship with the vapors ascending in the coil 24.

It is to be noted that as the stream of vapors passes upwardly within the coil 24, the portions thereof adjacent the inner side of the coil 24 are subjected to a cooling action by the liquid in the jacket 32, while those portions of the vapors adjacent the outer side of the coil 24 are not sublected to this cooling action but are prevented from cooling by the heat insulating material 39. Thus at every cross section of the stream of vapors in the coil 24, there is established a temperature gradient diametrically across the stream with the vapors on the inner side of the stream being cooled more than the vapors on the outer side of the stream.

The temperature and rate of passage of the cooling medium through the cooling Jacket 32 are adjusted so thatvapors of the desired conaasasee densing point or range of condensing points are condensed by the passage of the mixture of vapors through the coil 24, the condensate being either withdrawn through a condensate withdrawal pipe 4i connected through a suitable trap 42 with the coil 24 adjacent its lower end or returned through the bubble plates it to the still 2|, as may be desired. The trap 42 may be of any desired construction, such as a float controlled valve or steam trap, passing liquid therethrough but preventing the passage of vapor therethrough.

As the vapors condense upon the inner side of the wall 24, the condensate flows downwardly therethrough in a thin film. The surface upon which the vapors thus condense is made extremely large by virtue of the shape of the apparatus described. For example, in a coil of a three foot diameter comprising forty turns of pipe with a six inch internal diameter, there are presented approximately 570 square feet of surface for contact by the vapors. The condensate flowing downwardly in a thin film' on the inner side of the coil 24 is, throughout its travel in the coil, in intimate contact with and commingled with the ascending vapors. This intimate commingling of the descending reflux condensate and the ascending vapors insures an exchange between them, so that the lower boiling fractions of the liquid condensate are vaporized and the higher boiling fractions of the vapor are condensed within the coil 24. Since the path of travel of the vapors is very long within the tower 42, the temperature gradient longitudinally within the coil can be made very gradual, and a most accurate separation of the vapors can be achieved.

Tests of the method of my invention performed by apparatus such as described demonstrate a very accurate and complete separation of a mixture of hydrocarbon vapors of condensing points differing but slightly from each other. It is my belief that this is in part due to the fact that, in accordance with my invention, the vapors are passed in a spiral path, and a temperature gradient across each part of the path is maintained with the temperature of the vapors on the inner side of the spiral path or stream at a lesser value than the temperature of the vapors on the outer side of the spiral path or stream.

While I, do not desire to be restricted to the theories herein set forth, it is my belief that the accurate fractionation in accordance with my invention of a mixture of vapors of condensing points differing but slightly from each other is at least inpart due to action in accordance with one or both of the above stated theories.

In Fig. 3 there is illustrated an alternative embodiment of my invention in which the parts like those previously described are identified by like numbers. This embodiment of my invention differs from the embodiment illustrated in Figs. 1 and 2 in that the insulating material 39 is omitted, and there is provided around, the coil 24 and within the tower l2 a heating medium 43. The heating medium 43 may be of any desired material, such as steam, and is circulated through the tower l2 in intimate contact with the outer surface of the coil 24 by an inlet pipe 44 and an outlet pipe 45.

In many applications of my invention, such as the embodiment illustrated in Fig. 3, the supplying of heat to the outer surface of the coil 24 establishes a sharper temperature gradient across the coil and provides improved separation of the vapors, In this embodiment oi my invention, as in that previously described, the heat conducting relationship of the cooling jacket 32 with the coil 24 may be improved by filling the spaces between them, indicated by the numeral 46, with a material of high heat conductivity. such as a suitable metal.

The embodiment of my invention illustrated in Fig. 4 diiiers from the embodiment illustrated in Fig. 1 in that there is substituted for the cooling jacket 32 of the form shown in Fig. l a cooling coil 41, each convolution of which is positioned between and in contact with two convolutions of the vapor coil 24, so that each convolution of the coil 41 is in heat transferring relationship with two convolutions of the vapor coil 24.

In the form of apparatus of my invention illustrated in Fig. 5, adjacent convolutions of a coil 48 for vapors are connected in fluid-tight relationship as by welding 45, the whole of the space 50 within the coil 48 beingavailable for the circulation of a cooling medium.

The still 2i and the bubble plate chamber l1 may be constructed separately from the tower i2 and separate from each other without departing from my invention. Likewise, there may be substituted for the bubble plates l8 in the chamber l1 other means of smoothing out the flow of vapors, such as Raschig rings. iullers earth, bauxite, iron turnings, etc.

Further. a plurality of liquid outlet lines may be connected to the coil at different levels, each withdrawing the condensate of vapors having a definite condensing point or range of condensing points.

From the foregoing it will be seen that the method of my invention contemplates the passage or a mixture of vapors of different condensing points in a curved path so that each section of the stream has a temperature gradient thereacross with the lower temperature at the inner side of the curved path or stream and the higher temperature at the outer side, and with a temperature gradient along the stream with the higher temperature at the source of the stream, and the commingling of the reflux condensate with the vapors along the walls defining the curved path of the stream through the length of the stream. It will also be seen that my invention contemplates the selective condensation of a liquid which may be a mixture of hydrocarbons all of which boil within narrow temperature limits, or would ordinarily be defined as having a narrow boiling point range, from a mixture oi. gases which contains said liquid in its gaseous phase, the initial mixture, of course, having a wider boiling point range than the liquid, but which includes that of the liquid. that portion or the mixture which is not so condensed passing through the process as a gas. In the process illustrated and described, the condensation takes place in a helical passage which is provided by the pipe coil. and the condensation takes place wholly upon the inner wall of the helix formed by the coil, that is, upon the wall nearest the axis of the helix, due to the fact that this inner portion of the wall is cooled below the temperature of the remainder of the wall, or, what amounts to the same thing, the remainder of the wall is hotter than the condensing surface thereof.

Various modifications of the method and apparatus of my invention will occur to those skilled in the art, and my invention must be understood therefore as not restricted to the embodiments, steps, or applications hereinbefore specifically set forth.

I claim as my invention:

1. A process of selectively condensing a liquid having a narrow boiling point range from a mixture of gases containing said liquid in its gaseous phase, said mixture having a wider boiling point range than said liquid, which comprises: passing said mixture of gases into the lower end of a closed passage of helical contour so disposed that any liquid condensed in said passage flows by gravity to the lower end thereof, and the mixture or gases rises through the passage; and cooling a' portion of the wall of the helical passage on the side nearest the axis oi! the helix to a sufllcient degree to cause a condensation from said mixture of the desired liquid, that portion of the mixture not so condensed passing while still in gaseous form out 01' said passage.

2. A process of selectively condensing a liquid having a narrow boiling point range from a mixture oi! gases containing said liquid in its gaseous phase, said mixture having a wider boiling point range than said liquid, which comprises: passing said mixture oi. gases into the lower end of a closed passage of helical contour so disposed that any liquid condensed in said passage flows by gravity to the lower end thereof, and the mixture of gases rises through the passage; and cooling a portion of the wall of the helical passage on the side nearest the axis 01' the helix to a lower temperature than the remainder of said wall and to a sufficient degree to cause a condensation from said mixture of the desired liquid, that portion 0! the mixture not so condensed passing while still in gaseous form out of said passage.

3. A process of selectively condensing a liquid having a narrow boiling point range from a mixture oi gases containing said liquid in its gaseous phase, said mixture having a wider boiling point range than said liquid, which comprises: passing said mixture of gases into the lower end of a closed passage of helical contour so disposed that any liquid condensed in said passage flows by gravity to the lower end thereof, and the mixture of gases rises through the passage; and cooling a portion of one vertical wall of the helical passage to a suflicient degree to cause a condensation from said mixture of the desired liquid, that portion of the mixture not so condensed passing while still in gaseous form out of said passage.

4. A process of selectively condensing a liquid having a narrow boiling point range from a mixture of gases containing said liquid in its gaseous phase, said mixture having a. wider boiling point range than said liquid, which comprises: passing said mixture of gases into the lower end of a closed passage of helical contour so disposed that any liquid condensed in said passage flows by gravity to the lower end thereof, and the mixture of gases rises through the passage; and cooling a portion of one vertical wall of the helical passage to a lower temperature than the remainder of said wall and to a suiilcient degree to cause condensation from said mixture of the desired liquid, that portion of the mixture not so condensed passing while still in gaseous form out of said passage.

FIDRIAN V. A'I'KESON. 

